AT&T sent shockwaves through the tech community last week when it announced its future plans for iOS 6’s new FaceTime over Cellular feature. The good news is that it won’t be charging separately for the service, but the bad news is only customers on its new Mobile Share data plans will be able to use it.

As you can imagine, this has folks upset — particularly AT&T customers who are still on unlimited, or other legacy, data plans. Why should they have to switch to a [likely] more expensive data plan to use the feature? Well, according to Public Knowledge’s senior lawyer John Bergmayer, they shouldn’t have to…

“Public Knowledge, a nonprofit group that focuses on Internet law, says that by prohibiting its other customers from using the video-calling feature on the network, AT&T is violating net-neutrality rules by blocking a service that potentially competes with its own.

John Bergmayer, senior staff lawyer at Public Knowledge, said AT&T was violating the F.C.C.’s Open Internet Rules, which say that mobile providers shall not “block applications that compete with the provider’s voice or video telephony services.”

AT&T, of course, is maintaining that it has done nothing wrong. Here’s a statement from Mark Siegel, a spokesman for the carrier:

“FaceTime is available to all of our customers today over Wi-Fi, and now we’re expanding its availability even further as an added benefit of our new Mobile Share data plans.”

The F.C.C. (Federal Communications Commission) has thus far not commented on the situation, but don’t count it out. The agency has been known to get involved with carrier affairs — most recently, telling Verizon it could no longer block third-party tethering applications and fining it $1.25 million.

It’ll be interesting to see how this unfolds, both from a legal and customer turnover standpoint. Apple is launching a new smartphone next month, and AT&T is already expected to lose a number of customers in favor of Verizon’s much larger LTE network. And this can’t possibly be helping its cause.